The present invention relates to a semiconductor device and a method for producing the same, in particular, a high dielectric constant film used for a gate insulating film.
With recent technological advance with respect to high integration and high speed in semiconductor devices, miniaturization of MOSFETs has been under development. When the thickness of a gate insulating film is being reduced to achieve the miniaturization, problems such as an increase of a gate leak current due to tunneling current are caused. In order to suppress this problem, there has been research on an approach to increase a physical thickness while realizing a small SiO2 equivalent thickness (hereinafter, referred to as “EOT”) by using gate insulating films made of high dielectric constant material such as hafnium oxide (HfO2) and zirconium oxide (ZrO2) (hereinafter, referred to as “high-k gate insulating films”).
For example, a method for forming a conventional high-k gate insulating film described in U.S. Pat. No. 6,013,553 is as follows. First, an oxide layer such as a SiO2 layer is formed on a silicon substrate, and then a metal film made of zirconium or hafnium is deposited on the oxide layer by sputtering or plasma CVD. Thereafter, the metal film is subjected to an oxynitridation treatment with gas such as NO to form a high-k gate insulating film made of zirconium oxynitride (ZrOxNy) or hafnium oxynitride (HfOxNy).
However, in the conventional high-k gate insulating film, when heat history is applied by a high temperature treatment during the production process, the high dielectric constant material constituting the gate insulating film is crystallized, so that the electrical conductivity via the resultant crystal grain boundaries or the defect level increases leak current. That is to say, the thermal stability of the conventional high-k gate insulating film is insufficient.